1. Field of the Invention
The subject invention relates to mechanical strain relief, and more particularly to strain relievers for tubes.
2. Description of Related Art
Metal tubing is used throughout gas turbine engines, e.g. for aircraft engine fuel injector test instrumentation like thermocouples and strain gauges. These gauges are typically coupled through thin-walled metal tubing to measurement instruments. The tubing can convey hot gases, liquids or fuel between sampling points and measurement instruments, and typically terminates at a junction where a joint boss welded or brazed to the tubing terminates the tubing run.
When a tube is subjected to repeated physical forces that exert bending forces or strain on the tube, the tube or tube joint can break. This is because a force applied at a distance from a tube junction has maximum effect on the tube at the tube wall portion adjacent the junction. Fatigue damage from tube vibration also accumulates most rapidly at the tube wall portion adjacent the tube junction as the junction fixes and damps the tube at the junction, thereby forcing the tube to flex at the tube wall portion. These forces are particularly problematic for test instrumentation of engines where the temporary installations may experience rough handling and the vibratory provisioning provided for tubing permanently installed in the engine. And in the case of a welded or brazed tube junction, the tube wall immediately adjacent the junction may also be of inferior strength compared to the remainder of the tube due to heat exposure during the joint boss attachment process or the material composition of the joint. These tubes therefore tend to shear off at the tube junction or termination due to the concentration of stress in these locations.
While the traditional techniques have been satisfactory for their intended purpose, there is a need for improved strain relief method and devices for tubes and tube junctions. There is also a continuing need for tube and tube junction strain relief methods and devices that are easy to make and use. The present invention provides a solution for these problems.